Method of moulding racquets with stringing holes

ABSTRACT

A method of moulding racquets to define stringing holes in the moulded frame. The method includes forming at least one approximately ladder-shaped member having two side pieces interconnected by rung pieces, with the side pieces substantially conforming to the curved shape of at least part of the frame of the racquet; entrapping the ladder-shaped member between two mould plates defining a mould cavity; injecting a plastic material into the mould cavity to mould the frame around the rung pieces; and forming the ladder-shaped member in two parts and separating the two parts after the frame has been moulded to remove the ladder-shaped member from the moulded frame.

This application is a continuation of application Ser. No. 096,336,filed Sept. 15, 1987 now U.S. Pat. No. 4,842,798.

This invention relates to racquets for use in games such as tennis,squash, racquet-ball and the like. The invention is more particularly,but not exclusively, concerned with methods of making fibre-reinforcedmoulded racquet frames.

It is known to mould racquet frames in fibre-reinforced thermoplasticsmaterial, with the fibre reinforcement taking the form of continuousfilamentary material woven into a fabric or braid. However, currentlyavailable methods of producing such moulded racquet frames suffer from anumber of disadvantages. In particular, it is both difficult andtime-consuming to provide frames moulded by these methods with stringingholes. It is therefore an object of the present invention to providemethods of making moulded racquet frames, particularly fibre-reinforcedmoulded racquet frames, in which this particular disadvantage isalleviated.

According to one aspect of the invention, there is provided a method ofmaking a moulded racquet, the method comprising the steps of:

forming at least one approximately ladder-shaped member having two sidepieces interconnected by rung pieces, the side pieces being curved inthe plane containing the rung pieces to substantially conform to thecurved shape of at least part of the frame of the racquet;

entrapping said member between two mould plates containing a mouldcavity shaped to define the frame, such that the rung pieces extendacross the mould cavity to define stringing holes passing through themoulded frame; and

injecting a suitable plastics material into the mould cavity to mouldthe frame around said rung pieces;

wherein the ladder-shaped member is formed in two parts which eachcontain a respective one of the side pieces and which are separablyfitted together to form the ladder-shaped member, said parts also beingmoulded from a suitable plastics material and being separated from eachother after the moulding of the frame to permit removal of theladder-shaped member from the moulded frame.

Advantageously, a single ladder-shaped member, shaped to conform to thewhole of the region of the frame containing stringing holes, is used.

In a preferred implemention of the invention, the side-piece of theladder-shaped member adjacent to the portion of the mould cavitydefining the radially outer surface of the frame is arranged to projectinto the mould cavity, so as to form a groove in the radially outersurface of the moulded frame.

The two parts making up the ladder-shaped member preferably fit togetheralong a line passing through each rung piece, typically at or near themid-point of each rung piece. Thus, the end of each rung piece portionprojecting from one side piece can be provided with a projection whichfits into a socket provided in the end of each corresponding rung pieceportion projecting from the other side piece.

If it is desired to make a fibre-reinforced moulded racquet frame, thenadvantageously two cores, each including a tube comprising at least onelayer of woven reinforcing fibres, are placed in the mould cavity, oneon each side of the ladder-shaped member (i.e. one on each side of thesplit line of the mould) prior to the closure of the mould onto theladder-shaped member. In this case, the plastics material injected intothe mould cavity is preferably a plastics material having a relativelylow setting temperature and a relatively low viscosity, such as amethacrylate-based resin.

Each core can comprise an inflatable tube disposed inside the tube ofreinforcing fibres, in which case the method can further include thesteps of inserting each inflatable tube, either uninflated or lightlyinflated, into its tube of reinforcing fibres prior to placing the coresinto the mould, and maintaining the inflatable tubes inflated during theinjection and setting of the plastics material.

Alternatively and preferably, each core can comprise a plastics foamcore member, advantageously an extruded polyethylene foam core member,disposed inside its tube of reinforcing fibres, in which case the methodcan advantageously further include the step of weaving each tube ofreinforcing fibres, preferably in the form of a braid, around its coremember.

The reinforcing fibres can be carbon fibres, boron fibres, glass fibres,silicon carbide fibres or aramid fibres of the kind available under thetrade name Kevlar, or any combination of these.

Where the tubes of reinforcing fibres are woven into a braid, they arepreferably woven in two contrasting colours, for example by using blackcarbon and yellow Kevlar fibres. This has the effect of producing astriking finished appearance for the frame, as will become apparenthereinafter.

The invention will now be described, by way of example only, withreference to the accompanying drawings, of which:

FIG. 1 is a somewhat schematic sectional view of part of a mould formaking a fibre-reinforced moulded racquet by a method in accordance withthe present invention;

FIG. 2 is an equally schematic, part-sectional, part-perspective view ofpart of the mould of FIG. 1;

FIG. 3 is a plan view of a ladder-shaped member for use in the mould ofFIG. 1;

FIG. 4 is a detailed part sectional view of the ladder-shaped member ofFIG. 3; and

FIG. 5 is a plan view of part of a finished racquet frame moulded in themould of FIGS. 1 and 2.

The mould shown in part in FIGS. 1 and 2 is indicated generally byreference 10, and comprises upper and lower complementary mould plates12 and 14 which together define a mould cavity 16 shaped to mould aracquet of the kind indicated at 18 in FIG. 5, this racquet having aframe 20 and a handle 22.

The overall shape of mould plates 12 and 14 in plan view generallycorresponds to the overall shape in plan view of the frame 20 and thehandle 22 of the racquet 18 of FIG. 5, which in turn is shaped generallyas shown more completely in FIG. 1 of United Kingom Patent ApplicationNo. 8426226 (Publication No. 2 148 133A): FIG. 1 hereof is a sectionalview of the part of the mould 10 which defines a curved portion of theframe 20 generally opposite the handle 22.

As can best be seen in FIG. 1, the mould plates 12 and 14 meet at asplit-line (or split-plane) 24, and are shaped to entrap between them aplastics ladder-shaped member 26, thus dividing the mould cavity 16 intoupper and lower halves 16a and 16b respectively. The member 26 comprisesfirst and second curved side pieces 28, 30 curved to follow thecurvature of the mould cavity 16, as best seen in FIG. 2.Interconnecting the side pieces 28 and 30 are spaced apart rung pieces32, which extend across the mould cavity 16 in the split-plane 24, andwhose purpose is to define stringing holes passing generally radiallythrough the frame 20 of the racquet 18 of FIG. 5.

The portions of the mould plates 12, 14 defining the right hand side ofthe mould cavity 16 as viewed in FIG. 1 (which side defines the radiallyinner periphery 34 of the frame 20 of the racquet 18 of FIG. 5) arerecessed to fully receive the side piece 30 of the member 26. Similarly,the portion of the mould plates 12,14 defining the left hand side of themould cavity 16 as viewed in FIG. 1 (which side defines the radiallyouter periphery 36 of the frame 20 of the racquet 18 of FIG. 5) are alsorecessed, to receive the side piece 28 of the member 26. However theside piece 28 is substantially wider, as viewed in FIG. 1, than the sidepiece 30, and is only partially received in its recess: the remainder ofthe side piece 28 protrudes into the mould cavity 16, to define astringing groove extending around the radially outer periphery 36 of theframe 20 of the moulded racquet 18.

The ladder-shaped member 26 is shown in more detail in FIGS. 3 and 4,from which it can be seen that the side piece 28 is provided with anoutwardly projecting spigot 40 (FIG. 3) which co-operates with acorresponding recess (not shown) in one of the mould plates 12, 14, toensure that the member 26 can be placed in the mould 10 in only oneorientation, i.e. the correct orientation. As shown in FIG. 4, themember 26 is made in two separate pieces, which join together along aline passing through the middle of each rung piece 32. To this end, theend of each half rung piece 32 projecting from the side piece 28 isprovided with a projecting spigot 42 which is received into, and is atight fit in, a complementary socket 44 provided in the end of thecorresponding half rung piece 32 projecting from the side piece 30.

The member 26 is made from a suitable plastics material such as PTFE.

The frame 20 and handle 22 of the racquet 18 are reinforced bycontinuous woven reinforcing fibres, preferably a combination of carbonfibres for tensile and flexural strength and Kevlar fibres for impactresistance. The carbon fibres are black, while the Kevlar fibres areyellow, and respective bundles of both fibres are preferably woventogether into a multi-layer tubular braid having a strikingly zig-zagstriped appearance of the kind shown in FIG. 5. The braid forms part ofa core, which is produced by weaving successive layers of fibres, eachlayer containing both kinds of fibres, onto an extruded polyethylenefoam core member, until a braided tube, four or five layers thick, iswoven onto the core member.

The weaving technique involved is known per se, e.g., for the weaving ofboot- or shoe-laces on a fibre core, and involves pulling the coremember along the centre line or axis of a multi-spindle braiding machinewhile weaving the first layer therearound, then passing the core memberwith the first layer of braid on it through the same braiding machineagain to weave the second layer therearound, and so on. To give addedtensile strength, a layer of longitudinally-extending fibres is appliedto the core, preferably between the penultimate and the final braidedlayers.

The weaving of the braid onto the core member ensures an extremely tightfit therebetween, so that the braid and core member form an almostintegral structure with significantly greater integration between thebraid and the core member than can be achieved by simply inserting thelatter into the former after weaving (particularly bearing in mind thatif the braid were separately woven to be such a tight fit on the coremember, it would probably not be possible to insert the core member intoit).

It will be appreciated that the core can be continuously produced asdescribed above to form considerable continuous lengths thereof, whichare typically wound into drums. Then, when required, any desired lengthof core is simply unwound and cut from the drum.

To mould the racquet 18, a first cut length of the aforementioned coreis laid in the lower half 16b of the mould cavity 16 in the lower mouldplate 14. The ladder-shaped member 26 is then mounted in the lower mouldplate 14, with the lower halves of its side pieces 28 and 30 located intheir respective half recesses therein. A second cut length of theaforementioned core is laid on top of the rung pieces 32 of the member26, and the mould 10 is then closed by closing the upper mould plate 12onto the lower mould plate 14 as shown in FIG. 1. Preferably, the wallsof the mould cavity 16, and the member 26, are sprayed with a releasingagent prior to and during loading the mould 10, to facilitate theremoval of the moulded racquet 18 from the mould after the mouldingoperation.

Once the mould 10 is assembled in its closed condition, a low viscosity,low temperature setting plastics material in the form of amethacrylate-based resin is injected into the mould cavity 16 underpressure. We have found that a particularly suitable resin is thatavailable from the Mond division of ICI under the trademark "Modar 835",which is a high molecular weight methacrylate-based resin in methylmethacrylate solution. It has a viscosity of 40 cps at 20 deg. C. Theresin is typically injected at a pressure of 30 p.s.i. and maintained ata temperature of 20 deg. C. during curing (or setting), under whichcondition it sets, and the mould 10 can be opened to remove the racquet18, in about four minutes. However, if the resin is maintained at ahigher temperature of about 85 deg. C. it sets in about one minute.

Even the higher temperature of 85 deg. C. is not sufficient to produceany interaction between the resin and the plastics material of theladder-shaped member 26.

Because of its low viscosity, the methacrylate resin not only penetratesthe weave of the reinforcing fibres of the two cores, but also forms athin layer between the cores on the one hand and the walls of the cavity16. The formation of this thin layer of resin has the result that, whenthe mould 10 is opened, the resulting moulded racquet requires little orno further surface finishing to enhance its appearance.

Upon opening of the mould 10, the moulded racquet 18 is with theladder-like member 26 moulded into it. However the member 26 can beremoved from the racquet 18 simply by pulling its two halves apart, thusenabling the respective half rung pieces 32 attached to the side pieces28, 30 to be withdrawn from the frame 20, leaving stringing holestherein.

Once the member 26 has been removed from the racquet 18, its two halvescan be simply re-fitted together, thus enabling it to be used again.

As can be seen in FIG. 4, the connecting points between the rung pieces32 and the side pieces 28, 30 are suitably smoothly rounded or curved,to ensure that the entry and exit of each stringing hole arecorrespondingly smoothly rounded or curved around their respectiveperipheries and so prevent chafing of the strings of the racquet 18.

The frame 20 of the racquet 18 has the rather striking appearance shownin FIG. 5, with a smooth finish and a regular zig-zag pattern of thebraid clearly visible through the transparent resin; consequently,little or no surface finishing is necessary. All that remains tocomplete the racquet 18, therefore, is fitting a suitable grip (notshown) on the handle 22 and securing the stringing (not shown) to theframe 20 by way of the moulded in stringing holes.

It will be appreciated that the above described method of making theracquet 18 has a number of advantages. Primarily, it is relatively fastand clean, and produces a racquet frame that needs little or no furthersurface finishing and can if desired have a striking appearance.Additionally the use of carbon and Kevlar reinforcing fibres mean thatthe racquet 18, is light and strong, with good impact resistance.

Many modifications can be made to the above-described of making theracquet 18. For example, reinforcing fibres other than carbon and Kevlarcan be used, e.g. glass fibres, silicon carbide fibres or boron fibres,either on their own or in combination with each other. Various differentweaving patterns and colour combinations can also be used, to producedifferent visual effects or patterns in the surface of the finishedframe, e.g. diamond patterns, pepper-and-salt patterns and so on. Also,the cores described hereinbefore can each be formed with a hollowinflatable core member in place of a foam core member, this inflatablecore member being inserted into the braid while uninflated or onlypartially inflated, and then fully inflated during the moulding process.Furthermore, other suitable low temperature curing, low viscosity resinsor like plastics materials can be used in place of specific methacrylateresin cited including other resins in the "Modar" range of resinsoffered by ICI. Indeed a thermosetting plastics material can also beused, as long as it is selected not to interact with the plasticsladder-shaped member 26: however, in that case, some of the advantagesof the above-described method of making the racquet 18 would be lost.

I claim:
 1. A method for making a molded racquet frame having a curvedhead portion and a plurality of stringing holes in at least a part ofsaid head portion, the method comprising:disposing within a mold cavitya separable, curved, ladder-shaped member of two assembled parts, theassembled ladder-shaped member comprising two side pieces having aplurality of rung-shaped members disposed therebetween and beingpositioned in said mold cavity so that surfaces of the rung-shapedmembers will form said stringing holes passing generally radiallythrough said head portion and so that surfaces of said side piecesfacing said rung-shaped members will form outer and inner surfaces ofsaid curved head portion; injecting a plastic material into said moldcavity; removing the molded racquet frame and the ladder-shaped memberfrom within said mold cavity; and then separating said ladder-shapedmember into said two side pieces to remove the ladder-shaped member fromthe head portion of said racquet.
 2. A method according to claim 1wherein the disposing step further comprises:disposing a single curved,ladder-shaped member within said mold to conform to the whole of theregion of the frame which is to contain stringing holes.
 3. A methodaccording to claim 1 wherein the disposing step furthercomprises:disposing said ladder-shaped member within said mold so thatthe side piece of the ladder-shaped member adjacent the portion of themold cavity defining the radially outer edge of said frame projects intothe mold cavity to form a groove in the radially outer edge of saidframe.
 4. A method according to claim 1 further comprising before theinjecting step:placing a core within said mold cavity on each side ofsaid ladder-shaped member, each of the cores comprising a layer of wovenreinforcing fibers.
 5. A method according to claim 4 wherein each ofsaid cores comprises an inflatable tube and said method furthercomprises:inflating each said inflatable tube before placing each saidcore and said fibers within said mold cavity; and maintaining each saidtube in an inflated condition during the injecting step.
 6. A methodaccording to claim 4 wherein each core comprises a plastic core memberand said method further comprises:weaving reinforcing fibers around eachcore in the form of a braid before said core is placed within said moldcavity.
 7. A method according to claim 6 wherein the weaving is with twocontrasting colors.
 8. A method according to claim 1 wherein theseparating step is along a connection located in center portions of saidrung-shaped members.
 9. A method according to claim 1 furthercomprising:aligning said ladder-shaped member within said mold byfitting a projection on said ladder-shaped member into a socket adjacentsaid mold cavity.
 10. A method according to claim 1 wherein theinjecting step comprises:injecting a plastic material having a lowsetting temperature and low viscosity to mold said racquet frame aroundsaid ladder-shaped member.
 11. A method according to claim 10 whereinthe injecting step comprises:injecting a methacrylate-based resin.